Influence of Calcium on the Self-Assembly of Partially Hydrolyzed a-Lactalbumin

• Published in: Langmuir Vol. 20; no. 16; pp. 6841 - 6846
• Main Authors: Johanna F Graveland-Bikker, Johanna F Graveland-Bikker Richard Ipsen, Otte, Jeanette, de Kruif, Cornelis G
• Format: Journal Article
• Language: English
• Published: 25-06-2004
• Subjects: Bacillus licheniformis
• ISSN: 0743-7463
• DOI: 10.1021/la049579v

Self-assembly of *a-lactalbumin after partial hydrolysis by a protease from Bacillus licheniformis can result in nanotubular structures, which show many similarities to microtubules. Calcium plays a crucial role in this process. The objective of this investigation was to study the role of calcium in more detail. The kinetics of the hydrolysis step and the self-assembly step were monitored by respectively liquid chromatography-mass spectrometry and dynamic light scattering. The microstructure of the gels finally formed was investigated by transmission electron microscopy. This investigation demonstrates that calcium accelerated the kinetics of the self-assembly, but it had no effect on the hydrolysis kinetics. As a result of the accelerated self-assembly kinetics at a high calcium concentration, the time of gelation decreased as well. A minimum concentration of calcium needed to obtain the tubular *a-lactalbumin structures was determined. Below R = 1.5 (mole calcium/mole *a-lactalbumin), turbid gels with randomlike structure were obtained. Between R = 1.5 and R = 6, translucent gels with a fine stranded network of tubules were formed, while higher calcium concentrations had a negative effect on the tubule formation, resulting in amorphous structures. The optimum calcium concentration for *a-lactalbumin nanotube formation seemed to be around R = 3.